Ubuntu Phone was in the game early as well, but Canonical gave up on it a little while ago. They said the reason they gave up was that having the technology working was the easy part.
The big problem was getting key app developers and phone manufacturers on board. Those demanded large up front payments before they would consider it and Canonical wasn't in a position to fork over that kind of money. That's why they binned the whole phone project, including the Unity GUI.
The whole thing is really more of a marketing and developer relations problem than a technology problem, and it requires very deep pockets. Google has both the deep pockets and the existing business connections to make it work.
I can see this rendering the Chromebook market obsolete, where instead of a Chromebook you would simply get an external screen and keyboard for your phone, possibly in the form of a folding dock. I don't think it would completely take over the traditional laptop market, but it may chew around the edges of it more than Chromebooks were able to.